Some remarks about pseudo gap behavior of nearly antiferromagnetic metals

In the antiferromagnetically ordered phase of a metal, gaps open on parts of the Fermi surface if the Fermi volume is sufficiently large. We discuss simple qualitative and heuristic arguments under what conditions precursor effects, i.e. pseudo gaps, are expected in the paramagnetic phase of a metal close to an antiferromagnetic quantum phase transition. At least for weak interactions, we do not expect the formation of pseudo gaps in a three dimensional material. According to our arguments, the upper critical dimension d_c for the formation of pseudo gaps is d_c=2. However, at the present stage we cannot rule out a higher upper critical dimension, 2 < d_c <= 3. We also discuss briefly the role of statistical interactions in pseudo gap phases.Comment: 6 pages, accepted in PRB, relevant references added, several small change

Antiferromagnetism and single-particle properties in the two-dimensional half-filled Hubbard model: a non-linear sigma model approach

We describe a low-temperature approach to the two-dimensional half-filled Hubbard model which allows us to study both antiferromagnetism and single-particle properties. This approach ignores amplitude fluctuations of the antiferromagnetic (AF) order parameter and is valid below a crossover temperature $T_X$ which marks the onset of AF short-range order. Directional fluctuations (spin waves) are described by a non-linear sigma model (NL$\sigma$M) that we derive from the Hubbard model. At zero temperature and weak coupling, our results are typical of a Slater antiferromagnet. The AF gap is exponentially small; there are well-defined Bogoliubov quasi-particles (QP's) (carrying most of the spectral weight) coexisting with a high-energy incoherent excitation background. As $U$ increases, the Slater antiferromagnet progressively becomes a Mott-Heisenberg antiferromagnet. The Bogoliubov bands evolve into Mott-Hubbard bands separated by a large AF gap. A significant fraction of spectral weight is transferred from the Bogoliubov QP's to incoherent excitations. At finite temperature, there is a metal-insulator transition between a pseudogap phase at weak coupling and a Mott-Hubbard insulator at strong coupling. Finally, we point out that our results straightforwardly translate to the half-filled attractive Hubbard model, where the ${\bf q}=(\pi,\pi)$ charge and ${\bf q}=0$ pairing fluctuations combine to form an order parameter with SO(3) symmetry.Comment: Revtex4, 19 pages, 14 figures; (v2) final version as publishe

How long do nosocomial pathogens persist on inanimate surfaces? A systematic review

BACKGROUND: Inanimate surfaces have often been described as the source for outbreaks of nosocomial infections. The aim of this review is to summarize data on the persistence of different nosocomial pathogens on inanimate surfaces. METHODS: The literature was systematically reviewed in MedLine without language restrictions. In addition, cited articles in a report were assessed and standard textbooks on the topic were reviewed. All reports with experimental evidence on the duration of persistence of a nosocomial pathogen on any type of surface were included. RESULTS: Most gram-positive bacteria, such as Enterococcus spp. (including VRE), Staphylococcus aureus (including MRSA), or Streptococcus pyogenes, survive for months on dry surfaces. Many gram-negative species, such as Acinetobacter spp., Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa, Serratia marcescens, or Shigella spp., can also survive for months. A few others, such as Bordetella pertussis, Haemophilus influenzae, Proteus vulgaris, or Vibrio cholerae, however, persist only for days. Mycobacteria, including Mycobacterium tuberculosis, and spore-forming bacteria, including Clostridium difficile, can also survive for months on surfaces. Candida albicans as the most important nosocomial fungal pathogen can survive up to 4 months on surfaces. Persistence of other yeasts, such as Torulopsis glabrata, was described to be similar (5 months) or shorter (Candida parapsilosis, 14 days). Most viruses from the respiratory tract, such as corona, coxsackie, influenza, SARS or rhino virus, can persist on surfaces for a few days. Viruses from the gastrointestinal tract, such as astrovirus, HAV, polio- or rota virus, persist for approximately 2 months. Blood-borne viruses, such as HBV or HIV, can persist for more than one week. Herpes viruses, such as CMV or HSV type 1 and 2, have been shown to persist from only a few hours up to 7 days. CONCLUSION: The most common nosocomial pathogens may well survive or persist on surfaces for months and can thereby be a continuous source of transmission if no regular preventive surface disinfection is performed

QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe

OD approach to calcioaravaipaite, [PbCa2Al(F,OH)9]: the crystal structure of the triclinic MDO polytype

The crystal structure of calcioaravaipaite, PbCa2Al(F,OH)9, was initially solved by direct methods in the monoclinic space group A2/m (R = 12.4%). Further study demonstrated the OD nature of the structure, and showed that the crystal was twinned. The structure was solved in the triclinic space group C-1, a = 7.722(3), b = 7.516(3), c = 12.206(4) Å, α = 98.86(1), β = 96.91(1), γ = 90.00(1)°, V = 694.8(3) Å3, Z = 4, yielding R = 5.1% for 1420 reflections with F0 > 4σ(F0). Calcioaravaipaite belongs to a family of order-disorder (OD) structures formed by equivalent layers of symmetry C2/m. Two maximum-degree-of-order (MDO) polytypes are possible. MDO1 results from a regular alternation of stacking operators 21/2 and 21/2 yields a monoclinic structure with C2/c, a = 7.72, b = 7.52, c = 24.12 Å, β = 96.99°. MDO2 results from the sequence fluorite-like double layer of edge-sharing (CaF8) distorted cubes and slab 2 is a composite of face- and edge-sharing (PbF12) polyhedra and outlying (AlF6) octahedra, the latter sharing faces and edges with the (PbF12) polyhedra, but no elements with one another. Aravaipaite and calcioaravaipaite share a common fluorite-type layer; however, in avaraipaite the presence of Pb2+ rather than Ca2+ in this layer results in slabs of strikingly different polyhedral configuration

Laurelite: Its crystal structure and relationship to alpha-PbF2

Laurelite, Pb7F12Cl2, from the Grand Reef mine, Graham County, Arizona, is hexagonal, Pbar6, with a = 10.267(1) and c = 3.9844(4) Å and Z = 1. The crystal structure was solved by direct methods and refined to R = 0.035 and R(w2) = 0.089 for 693 measured reflections (Fo > 9 sigma(Fo)). The structure is related to that of alpha-PbF2. Both are based upon ninefold-coordinated Pb as tricapped trigonal prisms (TCTPs), which share edges and faces. The two structures can be described with respect to the face-sharing linkages of their TCTPs. The structure of alpha-PbF2 consists of corrugated sheets of face-sharing TCTPs that interlock by edge-sharing perpendicular to the c axis. In laurelite, the Pb2 TCTPs form three-membered face-sharing clusters about the threefold axis that are propagated into trigonal cylinders by sharing faces in the direction of the c axis. The Pb1 and Pb3 TCTPs are linked by face-sharing into a three-dimensional framework with corresponding cylindrical voids. Asymmetric coordinations about Pb1 and Pb2 are attributed to the stereoactive lone-pair effect. Although the coordinations about the anions appear to disallow substitution of OH for F, stacking defects along the c axis provide a mechanism for accommodating limited OH or H2O for F substitution. A new density determination yielded 7.65(5) g/cm3, in reasonable agreement with the density of 7.77 g/cm3 calculated on the basis of the empirical formula Pb0.97[F1.68Cl0.25(H2O)(0.07)], Z = 7

Discreditation of 'orthobrochantite' (IMA 78-64) as the MDO1 polytype of brochantite

"Orthobrochantite", IMA 78–64, was originally approved by the Commission on New Minerals, Nomenclature and Classification (IMA) as the orthorhombic polymorph of brochantite. Described by Wilson W. Crook III and Stanley G. Oswald from the Douglas Hill mine, Yerington, Nevada, USA, the mineral description was never formally published; however, the name and some data have been widely available since the late 1970s. Investigation of material from the Douglas Hill mine shows "orthobrochantite" to consist mostly of the MDO1 polytype of brochantite, but probably also to contain small domains of the MDO2 polytype. The crystal structure of the MDO1 polytype [a = 13.1117(4), b = 9.8654(4), c = 6.0307(9) Å, beta = 103.255(7)° and V = 759.31(12) Å3] has been refined to R1 = 6.37 % for 1245 unique reflections [Fo > 4(sigma)Fo] and 8.83 % for all 1724 reflections. The incorrect unit cell for "orthobrochantite" is either due to the choice of the B-centered pseudo-orthorhombic cell, which is virtually identical to the MDO1 cell, or indexing based on {100} twinning of the MDO1 polytype. New optical determinations for "orthobrochantite" suggest that the indices of refraction reported by Crook and Oswald were significantly in error

Nomenclature of the apatite supergroup minerals

The apatite supergroup includes minerals with a generic chemical formula IXM12VIIM23(IVTO4)3X (Z = 2); chemically they can be phosphates, arsenates, vanadates, silicates, and sulphates. The maximum space group symmetry is P63/m, but several members of the supergroup have a lower symmetry due to cation ordering and deviations from the ideal topology, which may result in an increase of the number of the independent sites. The apatite supergroup can be formally divided into five groups, based on crystal-chemical arguments: apatite group, hedyphane group, belovite group, britholite group, and ellestadite group. The abundance of distinct ions which may be hosted at the key-sites [M = Ca2+, Pb2+, Ba2+, Sr2+, Mn2+, Na+, Ce3+, La3+, Y3+, Bi3+; T = P5+, As5+, V5+, Si4+, S6+, B3+; X = F-, (OH)-, Cl-] result in a large number of compositions which may have the status of distinct mineral species. Naming of apatite supergroup minerals in the past has resulted in nomenclature inconsistencies and problems. Therefore, an ad hoc IMA-CNMNC Subcommittee was established with the aim of rationalizing the nomenclature within the apatite supergroup and making some order among existing and potentially new mineral species. In addition to general recommendations for the handling of chemical (EPMA) data and for the allocation of ions within the various sites, the main recommendations of this subcommittee are the following: 1. Nomenclature changes to existing minerals. The use of adjectival prefixes for anions is to be preferred instead of modified Levinson suffixes; accordingly, six minerals should be renamed as follows: apatite-(CaF) to fluorapatite, apatite-(CaOH) to hydroxylapatite, apatite-(CaCl) to chlorapatite, ellestadite-(F) to fluorellestadite, ellestadite-(OH) to hydroxylellestadite, phosphohedyphane-(F) to fluorphosphohedyphane. For the apatite group species these changes return the names that have been used in thousands of scientific paper, treatises and museum catalogues over the last 150 years. The new mineral IMA 2008-009, approved without a name, is here named stronadelphite. Apatite-(SrOH) is renamed fluorstrophite. Deloneite-(Ce) is renamed deloneite. The new mineral IMA 2009-005 is approved with the name fluorbritholite-(Y). 2. Potentially new mineral species. The following end-member compositions are eligible for status as distinct mineral species; the approved name, if any, is given in parentheses: Ca2Pb3(AsO4)3(OH) (hydroxylhedyphane); Ca2Pb3(PO4)3(OH) (hydroxylphosphohedyphane); Ca2Sr3(PO4)3F (new root name); Mn2Ca3(PO4)3Cl (new root name); Pb5(SiO4)1.5(SO4)1.5(OH) (hydroxylmattheddleite). 3. Minerals and mineral names which could be discredited. The mineral ellestadite-(Cl) is not thought to exist and should be discredited; the name melanocerite-(Ce) should be discontinued [= tritomite-(Ce)]. 4. Changes of status from distinct species to polymorphic variants. Fermorite is the monoclinic polymorph of johnbaumite (= johnbaumite-M); clinohydroxylapatite is the monoclinic polymorph of hydroxylapatite (= hydroxylapatite-M); clinomimetite is the monoclinic polymorph of mimetite (= mimetite-M). 5. Recognition of a new polymorphic variant. A new monoclinic polymorph of apatite is recognized (chlorapatite-M). 6. Changes to end-member formulae. The ideal chemical formula of morelandite is Ca2Ba3(AsO4)3Cl instead of Ba5(AsO4)3Cl; the ideal chemical formula of deloneite is (Na0.5REE0.25Ca0.25) (Ca0.75REE0.25) Sr1.5 (CaNa0.25REE0.25) (PO4)3 F0.5(OH)0.5